China's prime minister wrapped up his visit to Hong Kong Tuesday with a ceremony marking the sixth anniversary of the former British colony's return to Chinese sovereignty. But the morning's pageantry is likely to be overshadowed by a massive afternoon protest over proposed anti-subversion legislation.

Chinese Prime Minister Wen Jiabao and Hong Kong leaders looked on Tuesday as flags of the People's Republic of China and the Hong Kong Special Administrative Region were raised side by side. Patriotic music played as helicopters pulled flags through the sky, to mark the sixth anniversary of Hong Kong's return from Britain to China in 1997.

Police stopped 15 protesters from approaching the ceremony in what may be a small preview of Tuesday's main event: a massive street protest expected to attract tens of thousands of people.

Mr. Wen left late Tuesday morning, a few hours before the protest commenced.

The marchers oppose legislation to impose new anti-subversion laws. The protest is uniting journalists, business and religious leaders, who say the laws will provide China with a national security pretext for limiting Hong Kong's freedoms.

The prime minister says Hong Kong has no need to worry. Mister Wen says the laws will definitely not affect in any way the rights and freedoms enjoyed by Hong Kong people, including journalists.

He offered guarantees that China will not interfere with the autonomy granted Hong Kong under the "one country, two systems" policy it adopted at the return to Chinese rule. The policy means that Hong Kong retains its capitalist economy, British-style judicial system and far more individual freedoms than are allowed in mainland China.

Mr. Wen also urged Hong Kong people to create an environment favorable to international investment.

Pro-democracy politicians say they are disappointed by Mr. Wen's failure to respond directly to more specific questions about the anti-subversion law.

In a symbolic move aimed at getting the prime minister's attention, a small group of protesters burned a flag with the symbol of the Chinese Communist Party.

Burning the flags of China and Hong Kong has been illegal since 1997 - but there is no ban on burning the Communist Party flag, and police made no arrests. Protesters say they burned the flag to call for the end of one-party rule in China.

Mr. Wen's visit also included the signing of a free trade pact with Hong Kong, and a tour of areas hardest hit by the outbreak of Severe Acute Respiratory Syndrome, or SARS. He expressed regret that he did not visit the territory while the outbreak was underway.